1. Field of the Invention
The invention relates to an optical touch module, and more specifically, to an optical touch module capable of increasing a light emitting angle of a light emitting unit disposed therein.
2. Description of the Prior Art
In general, a conventional optical touch module utilizes a light interruption method or a direct image capturing method to detect a position of a user's finger on a touch surface. Both of the two methods utilize two (or three) image capturing devices and a near-infrared light emitting device. The said two image capturing devices are usually disposed at upper-left and upper-right corners of a touch screen, respectively. The difference between the two methods is that the light interruption method utilizes a background lighting design, in which a reflective bar or a near-infrared light emitting bar is disposed around the touch screen. In the light interruption method, a user's finger is taken as an interruption object for partially interrupting light, which is emitted from the reflective bar or the near-infrared light emitting bar, when touching the touch screen. At this time, a position of the user's finger on the touch screen can be calculated accordingly by utilizing the said image capturing devices to capture related optical images and then performing corresponding image processing. On the other hand, the direct image capturing method utilizes a near-infrared light emitting device to illuminate a user's finger directly instead of the said background lighting design. Subsequently, a position of the user's finger on the touch screen can also be calculated by utilizing the said image capturing devices to capture related optical images and then performing corresponding image processing.
Compared with the light interruption method, in which the length of the reflective bar or the near-infrared light emitting bar needs to be increased accordingly when the size of the touch screen is enlarged, the direct image capturing method is more suitable for a monitor with a large size (e.g. a 20-inch monitor). However, the area of the touch surface is also increased when the size of the touch screen is enlarged. Thus, if the direct image capturing method is applied to a monitor with a large size, uneven light distribution over the enlarged touch surface may occur since only part of the enlarged touch surface can be covered by light emitted from the near-infrared light emitting device. As a result, optical images in different regions on the enlarged touch surface are different from each other in brightness, so as to influence accuracy of the optical touch module in optical positioning. Furthermore, incorrect positioning or touch failure may also occur due to the exceeding light brightness differences on the touch surface.